This invention relates to chuck assemblies for tool bits, and more particularly, to a quick release chuck adapted to receive and retain a plurality of tool bits having varying shank cross-sectional sizes.
Tool bits include tools used for drilling and driving fastener devices such as screws, nuts and bolts, and other work elements requiring rotational motion. The traditional or “incremental” design typically consists of a mechanism that houses three adjustable jaws which protrude at an angle into a bore. An external sleeve is coupled to the jaws via internal gear teeth. When a tool shank is inserted into the bore, the sleeve is rotated by a user. As the sleeve is rotated in one direction, the jaws are forced towards the center of the bore to clamp a tool bit and tighten the sleeve into place (e.g. using a chuck key). When the sleeve is rotated in the opposite direction, the jaws are opened. This chuck style is able to accommodate a variety of tool shank sizes and shapes. However, changing a tool bit takes time and extensive operator involvement.
Tools having an alternate approach to chuck design allow for tool bits to be exchanged in a “quick-change” manner. The American National Standards Institute has a specification for such tools known as ANSI B 107.4-1982, which refers to driving and spindle ends for portable powered and hand-held machines which use tool bits. Tool bits in accordance with the standard have a hexagonally configured shank with a circumferential groove formed into the shank. The circumferential groove has a flat, bottom portion disposed between two radiused shoulder portions. The standard reflects an alternate and pervasive use of such tool bits and the large inventory of tools available.
One type of quick-change or quick-release chuck uses a spring biased sleeve disposed on a spindle or hub, as described in U.S. Pat. Nos. 4,900,202 and 5,013,194, both of which are incorporated by reference herein. Quick-release chucks of this type require the use of tools that have shanks of a consistent size (typically, ¼″ hex shank), usually having hexagonal cross sections. A spring biased sleeve is used to retain the tool bit in the chuck. The sleeve urges a detent ball into contact with the circumferential groove of the tool bit and maintains the ball in position by a shoulder (or cam surface) mounted on the sleeve. The ball is urged into contact with the groove and maintained in position by a compression spring disposed between the spindle and the sleeve. A ring secured to the hub limits movement of the sleeve in one direction, and the compression spring limits movement of the sleeve in the opposite direction.
The tool bit is prevented from being axially extracted from the chuck by the ball. The spring biased shoulder is urged against the detent ball which locks it against a retaining face on the tool bit. Attempting to extract the tool bit from the bore without release of the ball pulls the ball against the retaining face. The resulting force prevents extraction of the tool bit from the shank receiving bore. To release the tool bit from the receiving bore, the user must retract the sleeve. The retracted sleeve acts to compress the spring, which removes the shoulder from engagement with the ball and thereby allows the ball to move out of the circumferential groove of the tool bit. Thus, quick-release chucks allow for an operator to easily and quickly insert and remove tool bits from the chuck without requiring the use of a chuck key or requiring the loosening or tightening of jaws onto the shank of the tool bit.
Previous quick-release systems are only able to accommodate a single cross-sectional size tool bit shank. Thus, order to provide sufficient rotational torque, the cross-sectional size of the receiving bore of the quick-release chuck must be substantially the same as the cross-sectional size of the tool bit shank in order for the quick-release chuck to rotate the tool bit as the chuck rotates. A quick-release chuck assembly is needed in the art which quickly and efficiently exchanges tool bits having different cross-sectional sites.